The present invention is directed to an article sensor capable of detecting an article on an article holder and an article transfer device having such sensor. While such article sensor is provided to detect an article on an article holder, it is possible to use it to determine if an article is in a proper position by placing the sensor so that the sensor would not detect the article if the article is not in the proper position. Examples for the location for the article sensor include an article holder provided to the article transfer device, a conveyer, and an article receiving platform. The horizontally movable article holder is provided to an article transfer device, such as a folk device, which in turn is provide to a moving body, such as a stacker crane, capable of moving to different article transfer locations to transfer articles between itself and the transfer locations. See, for example, JP2000-219498.
Conventional article sensors use communication wiring connected to the destination device for communicating the detected information. When the article sensor is located on the article transfer holder, the controller controls the moving body, such as a stacker crane, based on the detected information from the article sensor communicated through the communication wiring connected between the sensor and the controller. The controller determines if the article on the holder is not in the proper position based on the detected information from the article sensor and prevent the article from falling during the transporting process by, for example, stopping the moving body if and when it determines that the article is not in the proper position.
With conventional article sensors, wiring work is necessary in addition to placing the article sensor in the system.
When the article sensor is provided to the holder for transferring articles, the holder moves repeatedly between a projected position and a retracted position and so, the communication wire needs to be arranged so that it can bend and extend during the movements, which adds to the wiring work.